It's just an altered dominant chord. It could take the place of almost any V7 chord in a progression, though I wouldn't do it without telling the person playing over it.

Someones knowledge of guitar companies spelling determines what amps you can own. Really smart people can own things like Framus because they sound like they might be spelled with a "y" but they aren't.

I like to substitute E7#9 for a lot of C major sounds, Bb dominant sounds and also, of course, for e minor and E dominant type sounds.

Tritone subs ftw.

I forgot to mention, again, to swap the #9 for a b9, especially in iio to V movement. Like in A (Harmonic) Minor, the note F just sits there while the other notes move around it causing the F to change function. It's a nice transition.